76 PALEONTOLOGY OF NEW YORK. 



PTERINOPBCTEN DI8PANDUS, 11. s]). 

 PLATE I. XXXII. FIGS. U, 12. 



Shell large, somewhat rhomboid-ovate, oblique, varying with the age of the 

 shell; length a little greater than the height; margins regularly curved, 

 extending behind. 



Left valve convex. Right valve depressed-convex, somewhat smaller 

 than the left, and proportionally longer. 



Hinge-line straight, less than the greatest length of the shell, nearly 

 central. 



Beaks ohtuse, little elevated, anterior to the middle, directed forward. 

 Umbonal region scarcely defined, moderately prominent, subtending a right 

 angle. 



Ears triangular, undefined; margins concave. Posterior ear larger than 

 the anterior. Anterior ear limited by an undefined sulcus and moderate 

 sinus; extremity rounded. In the right valve, the anterior ear is narrow, 

 acute, with a deep, angular byssal sinus. 



Surface ornamented by prominent, rounded radii, which alternate irregu- 

 larly with finer intercalated radii, and increase in size and number towards 

 the margin ; crossed by concentric strige, with more distant varices of growth 

 which crenulate the radii. The rays are stronger over the anterior slopes, 

 and are continued on the ears, somewhat finer on the posterior and stronger 

 on the anterior. In the right valve the strong rays are regularly duplicat- 

 ing, and are finer ami equal on the posterior ear, with a few stronger ones 

 on the anterior ear. 



Ligamental area narrow. 



Two left valves measure respectively 45 and 37 mm. in length, 42 and 

 44 nun. in height, hinge-line 40 and 30 mm. A right valve is 32 mm. in 

 length, 27 nun. in height, hinge-line 28 mm. Other specimens of the left 

 valve vary considerably, apparently according to age. 



This species differs from P. Vertumnus in its greater proportional height, 

 shorter hinge-line, abruptly rounded radii, and much sharper small intermediate 



